1. Field of the Invention
The present invention relates to a circuit for adjusting the charging rate of cell modules constituting cells in combination which have a high voltage, for example, for use as a power source for drive motors for electric motor vehicles such as hybrid cars. The term xe2x80x9ccharging ratexe2x80x9d as used herein means the percentage to which the cells in combination are charged relative to the full capacity thereof.
2. Description of the Related Art
Power sources conventionally mounted in electric motor vehicles, such as hybrid cars, for drive motors comprise secondary cells connected in series for use in combination. Because combinations of such cells must produce a high voltage usually of 200 to 300 V, for example, 60 to 80 lithium secondary cells each having an output of about 3.6 V are connected in series, or about 200 NiMH secondary cells each having an output of about 1.2 V are connected in series for use in combination.
It is desired that all the secondary cells in combination be equivalent in charged state. Suppose one secondary cell is 70% in charging rate, and another secondary cell is 50% in charging rate. In this case, the amount of electricity chargeable into these cells in combination is 30% which corresponds to the amount of charge for the cell with the charging rate of 70% when it is to be charged to the full. If the two cells are charged to an amount in excess of 30%, the secondary cell with the charging rate of 70% will be charged more than 100% to become greatly shortened in life. Consequently the combination of cells is also shortened in life.
Variations in the amount of electricity remaining in the secondary cells in combination are dependent on the efficiency (charge-discharge efficiency) of the individual cells. For example, suppose the secondary cells in combination are all 100% in charge efficiency and 99.0 to 99.5% in discharge efficiency. If the cells are charged at 10 Ah, charge of 10 Ah is stored in each cell. When the cells are subsequently discharged at 10 Ah, charge of 10.1 Ah (=10 Ah/0.990) is delivered from the cell with a discharge efficiency of 99.0%, and charge of 10.05 Ah (=10 Ah/0.995) is delivered from the cell with a discharge efficiency of 99.5%. Charge which is 0.05 Ah greater will then remain in the cell with the higher discharge efficiency of 99.5%. Accordingly, the amount of remaining electricity varies from cell to cell as a result of repetition of charge and discharge. Especially in the case of lithium ion secondary cells which are exceedingly high in charge-discharge efficiency, slight variations in charge-discharge efficiency result in a pronounced tendency for the cells to vary in the amount of remaining electricity.
Accordingly, a charging rate adjusting circuit 6 shown in FIG. 9 is used for discharging secondary cells having a greater amount of charge and thereby giving them the same amount of remaining electricity as those of smaller amount of charge. In the case of the circuit, one or a plurality of secondary cells constitute a cell module 70, and four cell modules are connected in series to provide a cell block 71. Two cell blocks 71 are further connected in series to provide cells in combination.
Voltage detecting lines 61 extend from the opposite terminals of each cell block 71 and from the points of connection between two of the cell modules 70 and are connected to a voltage measuring circuit 62. Opposite terminals of each cell module 70 are connected to a discharge circuit 63 which will be described below. The voltage measuring circuits 62, 62 and the discharge circuits 1 to 8 are connected to an unillustrated control circuit. The control circuit controls the discharge operation of the discharge circuits 1 to 8 based on voltage across each cell module 70 measured by the voltage measuring circuits 62, 62.
FIG. 10 shows an example of construction of the discharge circuit 63. When a photocoupler 64 is turned on, an on-off switch 65 comprising a MOSFET is closed, causing a current to flow from the cell module 70 to a discharge resistor 66, whereby the charging rate of the cell module 11 can be lowered.
With the charging rate adjusting circuit 6 shown in FIG. 9, the control circuit specifies the cell module(s) 70 of high charging rate based on the voltage measuring result obtained from the voltage measuring circuit 6262, turning on the photocoupler of the discharge circuit 63 connected to each module 70 of high rate. This reduces the cell module 70 of high rate in charging rate, making all the cell modules equivalent in charging rate.
However, the conventional charging rate adjusting circuit 6 must be provided with a discharge circuit 63 for every cell module 70 constituting the cells in combination, thereby making the circuit large in size, hence the problem of impairing reliability of circuit operation and of a higher cost.
An object of the present invention is to provide a charging rate adjusting circuit for a cell combination which is adapted to reduce the number of components.
The present invention provides a first charging rate adjusting circuit for a cell combination comprising a plurality of cell blocks each having a plurality of cell modules connected to one another in series, the circuit being adapted to provide one of a uniform charging rate and a uniform voltage to the cell modules. The circuit comprises:
first connecting/disconnecting means for connecting or disconnecting the cell blocks one another in series,
second connecting/disconnecting means for connecting or disconnecting one another in parallel the cell modules corresponding to one another in the cell blocks,
a plurality of discharge circuits each being connected to opposite electrodes of each of the cell modules constituting at least one cell block and performing discharge operation in response to a discharge command,
a voltage detection circuit for detecting voltage across each of the cell modules constituting at least one cell block, and
a control circuit for setting the first connecting/disconnecting means into connecting state and setting the second connecting/disconnecting means into disconnecting state in usual operation when the cell combination is operated as a power supply source, while for setting the first connecting/disconnecting means into disconnecting state and setting the second connecting/disconnecting means into connecting state when the charging rate of the cell modules are adjusted, and giving the discharge command to one or a plurality of discharge circuits based on detection result obtained by the voltage detection circuit.
With the first charging rate adjusting circuit of the present invention, in the usual operation, the first connecting/disconnecting means is set into connecting state and the second connecting/disconnecting means is set into disconnecting state. Accordingly, the plurality of cell blocks are connected to one another in series, whereby the overall cell combination is operable as a power supply source.
On the other hand, when the charging rate is adjusted, the first connecting/disconnecting means is set into disconnecting state and the second connecting/disconnecting means is set into connecting state. Accordingly, the plurality of cell modules corresponding to each other in the plurality of cell blocks are interconnected in parallel, and thereby charge moves from a cell module of high charging rate to a cell module of low charging rate. In this way, charge and discharge is conducted between the cell modules, with the result that the plurality of cell modules interconnected in parallel are uniformized in charging rate in the plurality of cell blocks. Variations in charging rate among the cell modules constituting each cell block still remains.
The charging rate of the cell module reflects a voltage value across the cell module with high correlation, and particularly lithium ion secondary cells have this pronounced tendency. Suppose one cell module constituting one cell block has a higher voltage across the module than the other cell modules constituting the one cell block. Then the control circuit will give a discharge command to a discharge circuit which is connected to opposite electrodes of the one cell module, or to opposite electrodes of a cell module connected to the one cell module in parallel.
When the discharge command is input to the discharge circuit to perform the discharge operation, charge moves to the discharge circuit from the one cell module of higher voltage across the module and one or a plurality of cell modules connected to the one cell module in parallel, to discharge these cell modules. As a result, these cell modules are the same as the other cell modules in charging rate. Thus all the cell modules constituting all the cell blocks are made equivalent in charging rate.
When the cell modules of the first charging rate adjusting circuit embodying the invention are adjusted in charging rates, a plurality of cell modules corresponding to each other in a plurality of cell blocks are connected in parallel to discharge these cell modules with one discharge circuit. Accordingly, since the adjusting circuit is provided with the same number of the discharge circuits as that of the cell modules constituting one cell block, the number of the discharge circuits becomes smaller than in the case of the conventional charging rate adjusting circuit which needs to be provided with a discharge circuit for every cell module constituting the cell combination. The discharging rate adjusting circuit of the invention should be provided with the first connecting/disconnecting means and the second connecting/disconnecting means. However, the discharge circuit comprises a number of electronic components, so that the decreased amount of the number of the components due to the reduced number of the discharge circuits is greater than the increased amount of the number of the components due to the provision of the first connecting/disconnecting means and the second connecting/disconnecting means. Consequently, the number of the components of the overall charging rate adjusting circuit becomes smaller than the conventional charging rate adjusting circuit.
Furthermore, with the first discharging rate adjusting circuit of the invention, the plurality of cell modules interconnected in parallel in the plurality of cell blocks can be made uniform in charging rate resulting from charge and discharge between the cell modules, to thereby reduce the variations of the charging rate among all the cell modules constituting the cell combination. The plurality of cell modules constituting each cell block are made uniform in charging rate as a result of the discharge operation of the discharge circuit. Accordingly, the amount of the abandoned energy resulting from the discharge operation of the discharge circuits can be smaller than in the conventional charging rate adjusting circuit wherein all the cell modules constituting the cell combination are uniformized in charging rate only by the discharge operation of the discharge circuit, thereby ensuring effective use of energy.
According to the first construction, the first connecting/disconnecting means comprises one or a plurality of serial lines for interconnecting a plurality of cell blocks in series and a first switch interposed on each serial line. The second connecting/disconnecting means comprises a plurality of parallel connecting points provided on opposite terminals of each of the cell blocks and on points of connection between the plurality of cell modules constituting each cell block, a plurality of parallel lines for interconnecting the parallel connecting points corresponding to each other in the cell blocks, and second switches interposed on each parallel line.
According to the first construction, in usual operation all the first switches are set on and all the second switches are set off, interconnecting the cell blocks in series. On the other hand, when charging rate is adjusted, all the first switches are set off and all the second switches are set on, interconnecting in parallel the cell modules corresponding to each other in the cell blocks.
For the prevention of short circuit of the cell modules, the first and second switches are each on-off controlled so that on periods of the first and second switches do not coincide. More specifically stated, when the first switch is set on, the second switch is always set off, or when the second switch is set on, the first switch is always set off.
Stated specifically, interposed on each of the parallel lines is a current limiting element for limiting a current value flowing into the second switch to a predetermined value or less. Usable as a current limit element is, for example, a resistor or a constant current value diode. According to the specific construction, even if there is a marked difference in charging rate among cell modules corresponding to one another in the cell blocks, a current having a greater value than the predetermined value will never flow into a second switch when the second switch is set on, to prevent the second switch from burning out owing to an excessive current.
According to a second specific construction, the first connecting/disconnecting means comprises one or a plurality of serial lines for interconnecting a plurality of cell blocks and a first switch interposed on each serial line. The second connecting/disconnecting means comprises a plurality of parallel connecting points each provided on opposite terminals of each cell block and on points of connection between two of the cell modules constituting each cell block, parallel lines each extending from each of the parallel connecting points of each of the cell blocks, and second switches each interposed on each of the parallel lines extending from the other cell blocks except one cell block or from each of all the cell blocks. A pair of positive and negative input terminals of the discharge circuit are respectively connected to a positive and a negative electrodes of each of all the cell modules corresponding to one another in the all cell blocks via the parallel line. Interposed on each of the parallel lines is a current limiting element for limiting a current value flowing into the second switch to a predetermined value or less. Usable as a current limiting element is, for example, a resistor or a constant current diode.
According to the second construction, in usual operation all the first switches are set on and all the second switches are set off, interconnecting the cell blocks in series. On the other hand, when charging rate is adjusted, all the first switches are set off and all the second switches are set on, interconnecting in parallel the cell modules corresponding to each other in the cell blocks.
For the prevention of a short circuit of the cell modules, the first and second switches are each on-off controlled so that on periods of the first and second switches do not coincide. More specifically stated, when the first switch is set on, the second switch is always set off, or when the second switch is set on, the first switch is always set off.
According to the second specific construction, even if there is a marked difference in charging rate among the cell modules corresponding to one another in the cell blocks, a current having a greater value than the predetermined value will never flow into the second switch when the second switch is set on, to prevent the second switch from burning out owing to an excessive current.
Further with the second specific construction, when each of the cell modules is discharged owing to the discharge operation of the discharge circuit, two current limiting elements are merely interposed on a path through which the discharging current flows. Accordingly, the two current limiting elements merely consume the power of the cell module, so that energy loss caused by the current limiting elements is suppressed, thereby ensuring the effective use of energy.
The present invention provides a second charging rate adjusting circuit for a cell combination comprising a plurality of cell blocks each having a plurality of cell modules connected to one another in series. The circuit comprises:
first connecting/disconnecting means for connecting or disconnecting the cell blocks one another in series,
second connecting/disconnecting means for connecting or disconnecting one another in parallel the cell modules corresponding to one another in the cell blocks,
a plurality of charge circuits each being connected to opposite electrodes of each of the cell modules constituting at least one cell block and performing charge operation in response to a charge command,
a voltage detection circuit for detecting voltage across each of the cell modules constituting at least one cell block, and
a control circuit for setting the first connecting/disconnecting means into connecting state and setting the second connecting/disconnecting means into disconnecting state in usual operation when the cell combination is operated as a power supply source, while for setting the first connecting/disconnecting means into disconnecting state and setting the second connecting/disconnecting means into connecting state when the charging rate of the cell module is adjusted, and giving the charge command to one or a plurality of charge circuits based on detection result obtained by the voltage detection circuit.
The second charging rate adjusting circuit of the invention described is provided with a charge circuit instead of a discharge circuit of the first charging rate adjusting circuit. When charging rate is adjusted, the first connecting/disconnecting means is set into disconnecting state, and the second connecting/disconnecting means is set into connecting state. Accordingly, the cell modules corresponding to each other in the cell blocks are interconnected in parallel, thereby uniformizing the cell modules in charging rate.
Suppose one cell module constituting one cell block has lower voltage across the module than the other cell modules constituting the one cell block. Then the control circuit will give a charge command to a charge circuit which is connected to opposite electrodes of the one cell module, or to opposite electrodes of a cell module connected to the one cell module in parallel.
When the charge command is input to the charge circuit to perform the charge operation, charge moves from the charge circuit to the one cell module of lower voltage across the module and to one or plurality of cell modules connected to the one cell module in parallel, to charge these cell modules. As a result, these cell modules are the same as the other cell modules in charging rate. Thus all the cell modules constituting all the cell blocks are made equivalent in charging rate.
When the cell modules of the second charging rate adjusting circuit embodying the invention are adjusted in charging rates, a plurality of cell modules corresponding to each other in a plurality of cell blocks are connected in parallel to charge these cell modules with one charge circuit. Accordingly, since the second charging rate adjusting circuit is provided with the same number of the charge circuits as that of the cell modules constituting one cell block, the number of the charge circuits becomes smaller than in the case of the charging rate adjusting circuit provided with a charge circuit for every cell module constituting the cell combination.
Furthermore, with the second charging rate adjusting circuit of the invention, charging rate is adjusted by allowing a cell module of lower charging rate to be charged, so that the amount of abandoned energy is zero, thereby ensuring the effective use of energy.
Stated specifically, the second charging rate adjusting circuit is provided with a charging battery for supplying power to the plurality of charge circuits. The power obtained from the charging battery is supplied to a cell module, charging the module. Alternatively, power input terminals of the charge circuits are connected to opposite terminals of one of the cell blocks, and the power obtained from one of the cell blocks is supplied to a cell module, charging the cell module.
As described above, the charging rate adjusting circuit for a cell combination of the invention is so adapted to reduce the number of components.